1. Field of Invention
This invention relates to methods and apparatus for full width, multi-color printing using a multi-pass printbar.
2. Description of Related Art
A carriage-type ink jet printer commonly has a plurality of printheads mounted upon a reciprocating carriage. Each printhead is provided with its own ink tank cartridge. Arrays of orifices in each printhead are aligned perpendicular to the line of movement of the carriage. One or more colors of ink are provided in each of the printheads. The respective ink colors are ejected from the printhead through the orifices and onto the recording medium, providing a swath of information printed upon a stationary recording medium. The printhead carriage is moved in one direction across the processing path of the recording medium when printing a swath.
After printing the initial swath, the recording medium is stepped, perpendicular to the line of the carriage movement, by a distance equal to or less than the width of the printhead swath. The carriage is then moved in the reverse direction to print another swath of information. When the second swath of printing is completed, the recording medium is again stepped, in a distance equal to or less than the width of the printhead swath. This process is repeated until the full page printing is achieved.
Multi-color printing systems having a plurality of single-color ink jet printhead arrays require precise alignment of the ink-ejecting orifices to produce the desired spacing for each of the ink colors which are deposited in swaths upon an output sheet. Various embodiments of linear printhead arrays include staggered linear arrays attached to a substrate and substantially horizontal linear arrays. Either is intended to provide full-width printing on an output sheet.
A monolithic approach to forming the printhead array usually comprises four or more full-width printbars, each printbar being used for one ink. In the case of four printbars, each printbar ejects one of black, cyan, magenta or yellow ink. In printing with full-width printbars, only one relative motion of the set of four printbars is used. That is, either the receiving sheet is moved and the set of four printbars is stationary, or the set of four printbars is moved and the receiver sheet is stationary.
Conventional carriage-type ink jet printers can be used to print up to approximately six pages per minute in high quality printing. In conventional carriage-type ink jet printers, the set of four printheads address where each picture element on the receiver sheet is and eject ink droplets at 300 resolution of spots per inch or better. On the other hand, a conventional full-width type ink jet printer can be much more productive than the conventional carriage-type ink jet printer, though a conventional full width printer is more expensive. Thus, when using a conventional full-width type ink jet printer, printing is faster, but becomes economical only when printing at 20 pages per minute (ppm) and higher. A productivity gap exists, therefore, for printing from 6 ppm to 20 ppm that is difficult to service by conventional carriage-type ink jet printers and for which conventional full-width type ink jet printers are not an economical alternative. This invention provides systems and methods that fill this productivity gap and that satisfy the need to print economically in the range of 6 ppm to 20 ppm, as well as at lower and higher page rates.
Multi-pass printbars provided with an array of ink-ejecting orifices are known to provide full width print coverage on a recording medium. The printhead dies in such known printbars are abutted immediately adjacent one another to avoid swath alignment errors, such as stitch errors. The adjacent printhead dies of known printbars are also known to provide unproductive swath overlaps in order to hide or eliminate swath alignment errors.
This invention provides multi-pass printing using a printbar having printhead dies that are spaced apart from one another while still providing full-width print coverage upon a recording medium. The printhead dies are provided with an array of ink-ejecting orifices similar to known printbars. However, the spacing of the dies uses movement of either, or both, of the printbar and the recording medium to produce the full-width printing effect.
In various exemplary embodiments of the full-width printbar apparatus and methods of this invention, the printbar having printhead dies spaced apart from one another is incorporated into a flatbed printing environment such that the recording medium remains stationary while the printbar moves over the recording medium to eject ink droplets upon the recording medium. In this embodiment, the printbar generates an initial set of swaths of information by ejecting ink from its array of ink-ejecting orifices while the array of spaced-apart printhead dies of the printbar is located, for example, at a first position.
After the initial set of swaths is completed, the printbar is stepped laterally to locate the array of spaced apart printhead dies at, for example, a second position where the next set of swaths of information is positioned, for each color in the next set of swaths, immediately adjacent to, or overlapping, the initial set of swaths of information for that color. The printbar undergoes successive stepping after the completion of each set of swaths until full-width print coverage is achieved on the recording medium. Alternatively, the flatbed printing environment supporting the recording medium can be stepped laterally instead of the printbar.
In various other exemplary embodiments, the printbar is stepped in successive swath widths while the recording medium is recirculated or reciprocated upon a drum or other recirculating or reciprocating document handler. Thus, for example, with each rotation of the drum, the printbar is stepped to the next position such that each succeeding set of swaths of information is imparted to the recording medium until full-width printing of the image upon the recording medium is achieved.
In still other various exemplary embodiments, the printbar is continuously moved in a linear fashion at a constant rate across a recording medium moving past the printbar upon a recirculating drum, or other recirculating or reciprocating document handler. Thus, for example, as the drum rotates the recording medium, the printbar""s constant linear motion permits ink to be ejected from orifices in its printhead dies to the recording medium similar to the various previously described exemplary embodiments. However, the linear motion of the printbar causes the swaths of ink ejected from the printhead dies to appear upon the recording medium in an angular, or xe2x80x9cbarber polexe2x80x9d, fashion when coupled with the motion imparted to the recording medium as a result of the recirculating drum, or other recirculating or reciprocating document handler.
In various exemplary embodiments, the receiving media may be placed on the drum or other document handler in an angled or slightly skewed fashion. The printbar is placed at a correspondingly small angled position relative to the recirculating axis of the document handler to achieve an optimum alignment of the printed images or text upon the receiving medium.
The combination of motions provide full-width print coverage upon the recording medium as the printhead dies will scan across the recording medium in time due to the continous and constant travel rate of the printbar while the drum moves the recording medium past the printbar. The angularly-oriented sets of swaths of information are provided in similar abutting, or overlapping, form as the various previously described exemplary embodiments to provide full width coverage. By controlling the rate of motions of the linearly moving printbar and the moving drums, proper swath alignment is achieved.
In still other various exemplary embodiments, the printbar, its printhead dies and ink-ejecting orifices remain stationary while the drum or other recirculating or reciprocating document handler is stepped after each set of swaths of information is completed. Stepping the drum occurs in swath-width or less increments until full-width print coverage upon the recording medium is achieved.
These and other features and advantages of this invention are described in or are apparent from the detailed description of various exemplary embodiments of the systems and methods according to this invention.